System and method for adjusting the speed of a multi-nozzle extruder during additive manufacturing with reference to an angular orientation of the extruder

ABSTRACT

An additive manufacturing system operates an extruder to extrude a swath of thermoplastic material through at least two nozzles of the extruder to form a swath of thermoplastic material along a path of relative movement between the extruder and a platform. The speed of the extruder along the path corresponds to a predetermined speed selected with reference to an orientation of the extruder and the angle for the path of relative movement between the extruder and the platform. A controller in the system operates at least one actuator operatively connected to at least one of the extruder and the platform to move the at least one of the extruder and the platform relative to the other of the extruder and the platform along the path of relative movement at the predetermined speed to make the swath of the thermoplastic material contiguous in a cross-process direction.

PRIORITY CLAIM

This application is a continuation of and claims priority to pendingU.S. patent application Ser. No. 15/817,588, which is entitled “SystemAnd Method For Adjusting The Speed Of A Multi-Nozzle Extruder DuringAdditive Manufacturing With Reference To An Angular Orientation Of TheExtruder,” which was filed on Nov. 20, 2017, and which issued as U.S.U.S. Pat. No. 10,682,816 on Jun. 16, 2020, the entirety of which ishereby expressly incorporated by reference.

TECHNICAL FIELD

This disclosure is directed to multi-nozzle extruders used inthree-dimensional object printers and, more particularly, to theformation of different features with such extruders.

BACKGROUND

Three-dimensional printing, also known as additive manufacturing, is aprocess of making a three-dimensional solid object from a digital modelof virtually any shape. Many three-dimensional printing technologies usean additive process in which an additive manufacturing device formssuccessive layers of the part on top of previously deposited layers.Some of these technologies use extruders that soften or melt extrusionmaterial, such as ABS plastic, into thermoplastic material and then emitthe thermoplastic material in a predetermined pattern. The printertypically operates the extruder to form successive layers of thethermoplastic material that form a three-dimensional printed object witha variety of shapes and structures. After each layer of thethree-dimensional printed object is formed, the thermoplastic materialcools and hardens to bond the layer to an underlying layer of thethree-dimensional printed object. This additive manufacturing method isdistinguishable from traditional object-forming techniques, which mostlyrely on the removal of material from a work piece by a subtractiveprocess, such as cutting or drilling.

Many existing three-dimensional printers use a single extruder thatextrudes material through a single nozzle. The printhead moves in apredetermined path to emit the build material onto selected locations ofa support member or previously deposited layers of the three-dimensionalprinted object based on model data for the three-dimensional printedobject. However, using a printhead with only a single nozzle to emit thebuild material often requires considerable time to form athree-dimensional printed object. Additionally, a printhead with alarger nozzle diameter can form three-dimensional printed object morequickly but loses the ability to emit build material in finer shapes forhigher detailed objects while nozzles with narrower diameters can formfiner detailed structures but require more time to build thethree-dimensional object.

To address the limitations of single nozzle extruders, multi-nozzleextruders have been developed. In these multi-nozzle extruders, thenozzles are formed in a common faceplate and the materials extrudedthrough the nozzles can come from one or more manifolds. In extrudershaving a single manifold, all of the nozzles extrude the same material,but the fluid path from the manifold to each nozzle can include a valvethat is operated to open and close the nozzles selectively. This abilityenables the shape of the swath of thermoplastic material extruder fromthe nozzles to be varied by changing the number of nozzles extrudingmaterial and which ones are extruding material. In extruders havingdifferent manifolds, each nozzle can extrude a different material withthe fluid path from one of the manifolds to its corresponding nozzleincluding a valve that can be operated to open and close the nozzleselectively. This ability enables the composition of the material in aswath to vary as well as the shape of the swath of thermoplasticmaterial extruder from the nozzles to be varied. Again, these variationsare achieved by changing the number of nozzles extruding material andwhich ones are extruding material. These multi-nozzle extruders enabledifferent materials to be extruded from different nozzles and used toform an object without having to coordinate the movement of differentextruder bodies. These different materials can enhance the ability ofthe additive manufacturing system to produce objects with differentcolors, physical properties, and configurations. Additionally, bychanging the number of nozzles extruding material, the size of theswaths produced can be altered to provide narrow swaths in areas whereprecise feature formation is required, such as object edges, and toprovide broader swaths to quickly form areas of an object, such as itsinterior regions.

In these multi-nozzle extruders having their nozzles in a commonfaceplate, the movement of the faceplate with reference to the buildplatform as well as the orientation of the faceplate with respect to theXY axes of the platform are critical to the formation of a swath. Asused in this document, a “swath” refers to the extrusion of materialfrom any opened nozzle in a multi-nozzle extruder as an aggregate aslong as at least one nozzle remains open and material is extruded fromany opened nozzle. That is, even if multiple nozzles are opened, but notall of the emitted extrusions contact one another, the discreteextrusions constitute a swath. A contiguous swath is one in which all ofthe extrusions from multiple nozzles are in contiguous contact acrossthe swath in a cross-process direction. At some orientations of theextruder, some of the nozzles align with one another in a way that mayprevent a contiguous swath of extruded material from being formed. Asshown in FIG. 7, a previously known faceplate having nine nozzles isdepicted. When the faceplate is oriented as shown in the figure andmoved along the 0°-180° (X) axis or the 90°-270° (Y) axis, all ninenozzles contribute to forming a contiguous swath and the swath has itsgreatest width. As used in this document, the term “0° 480° axis” meansmovement in either the 0° direction or the 180° direction with thefaceplate of the extruder oriented so if all of the nozzles are open,then the widest contiguous swath that the extruder can produce is formedand the term “90°-270° axis” means movement in either the 90° or the270° direction with the faceplate of the extruder oriented so if all ofthe nozzles are open, then the widest contiguous swath that the extrudercan produce is formed. When the faceplate remains oriented as shown onthe 0°-180° axis and 90°-270° axis, but moved in one of the directionsrotated 18° from one of these axis, as shown in the far rightillustration, the nine nozzles become three rows of three nozzles thatare aligned with one another and the swath is only three nozzles widewith gaps between the extruded lines forming the swath. Thus, the widestswaths are produced when the faceplate of FIG. 7 is moved along the 0°,90°, 180°, and 270° paths and the swaths are most narrow and the beadsof extruded material are most separated from one another along the 18°,108°, 198°, and 288° paths. The separation occurs because theorientation of the faceplate and the direction of the relative movementbetween the extruder and the platform arranges the nozzles in thefaceplate into an array having orthogonal columns and rows. Thisarrangement reduces the distance between the lines formed by the nozzlesin the columns so the lines align with one another and separates thelines by the spacing between the nozzles in a row. In the center of anobject where feature differentiation is usually unimportant, thefaceplate movement is preferred to be in one of the directions producingthe widest contiguous swaths so object formation speed can be maximized.At the outside edges of an object where feature shapes are more variedand sometimes intricate; however, fewer nozzles, and perhaps only asingle nozzle, may be opened to enable formation of the features.Unfortunately, this type of extruder operation does not capitalize onthe large number of nozzles available for object formation and isinherently slow. Thus, much of the speed advantage in having multiplenozzles in a common faceplate is lost and, for many parts, more time canbe spent on the outline of the object than was spent on the formation ofthe interior of the object. A three-dimensional object printer havingmultiple nozzles in a common faceplate that can exploit the number ofavailable nozzles at the formation of object exteriors would bebeneficial.

SUMMARY

A new extruder adjusts the speed of the extruder movement with referenceto the angle at which the faceplate is moved to enable multiple nozzlesto fill in the gaps between extruded lines to form exterior features.The apparatus includes a platform configured to support an object duringmanufacturing, an extruder having a plurality of nozzles, at least oneactuator operatively connected to at least one of the extruder and theplatform, the at least one actuator being configured to move the atleast one of the extruder and the platform relative to the other of theextruder and the platform, and a controller operatively connected to theextruder and the at least one actuator. The controller is configured to(1) operate the extruder to extrude a swath of thermoplastic materialthrough at least two of the nozzles of the extruder with reference toobject image data and extruder path data to form a swath ofthermoplastic material along a path of relative movement between theextruder and the platform, and (2) operate the at least one actuator tomove the at least one of the extruder and the platform along the path ofrelative movement at a predetermined speed, the controller selecting thepredetermined speed with reference to an orientation of a faceplate ofthe extruder and an angle for the path of relative movement between theextruder and the platform to make the swath of the thermoplasticmaterial contiguous in a cross-process direction.

A new method operates an extruder to adjust the speed of the extrudermovement with reference to the angle at which the faceplate is moved toenable multiple nozzles to fill in the gaps between extruded lines toform exterior features. The method includes operating with a controlleran extruder to extrude a swath of thermoplastic material through atleast two nozzles of the extruder with reference to object image dataand extruder path data to form a swath of thermoplastic material along apath of relative movement between the extruder and a platform thatsupports the object being formed with the thermoplastic material,selecting with the controller a predetermined speed for the relativemovement between the extruder and the platform with reference to anorientation of a faceplate of the extruder and an angle for the path ofrelative movement between the extruder and the platform, and operatingwith the controller at least one actuator operatively connected to atleast one of the extruder and the platform to move the at least one ofthe extruder and the platform relative to the other of the extruder andthe platform along the path of relative movement at the predeterminedspeed to make the swath of the thermoplastic material contiguous in across-process direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of systems that form objectswith thermoplastic material extruded from extruders are explained in thefollowing description, taken in connection with the accompanyingdrawings.

FIG. 1 depicts an additive manufacturing system that regulates a speedat which an extruder is moved to form a swath with reference to an angleof motion for the extruder.

FIG. 2 is a block diagram of an alternative embodiment of the systemshown in FIG. 1 that has only one heater with a plurality of channels.

FIG. 3 illustrates an operation of the extruder shown in FIGS. 1 and 2along a 342°-162° axis at different speeds to control the gaps betweenthe swaths produced by the extruder.

FIG. 4 illustrates an operation of the extruder shown in FIGS. 1 and 2along a 342°-162° axis at ⅓ normal speed to remove the gaps between theswaths produced by the extruder.

FIG. 5 is a flow diagram of a process for operating a printer thatadjusts the speed of extruder movement with reference to an angle ofextruder movement

FIG. 6 is a diagram of a prior art three-dimensional object printer.

FIG. 7 depicts swaths that can be formed by a nine nozzle faceplate whenoriented at 0°, 90°, and 18°.

DETAILED DESCRIPTION

For a general understanding of the environment for the device disclosedherein as well as the details for the device, reference is made to thedrawings. In the drawings, like reference numerals designate likeelements.

As used herein, the term “extrusion material” refers to a material thatis softened or melted to form thermoplastic material to be emitted by anextruder in an additive manufacturing system. The extrusion materialsinclude, but are not strictly limited to, both “build materials” thatform permanent portions of the three-dimensional printed object and“support materials” that form temporary structures to support portionsof the build material during a printing process and are then optionallyremoved after completion of the printing process. Examples of buildmaterials include, but are not limited to, acrylonitrile butadienestyrene (ABS) plastic, polylactic acid (PLA), aliphatic or semi-aromaticpolyamides (Nylon), plastics that include suspended carbon fiber orother aggregate materials, electrically conductive polymers, and anyother form of material that can be thermally treated to producethermoplastic material suitable for emission through an extruder.Examples of support materials include, but are not limited to,high-impact polystyrene (HIPS), polyvinyl alcohol (PVA), and othermaterials capable of extrusion after being thermally treated. In someextrusion printers, the extrusion material is supplied as continuouselongated length of material commonly known as a “filament.” Thisfilament is provided in a solid form by one or more rollers pulling theextrusion material filament from a spool or other supply and feeding thefilament into a heater that is fluidly connected to a manifold withinthe extruder. Although the illustrated examples use extrusion materialthat is supplied as filament to the heaters, other extrusion materialsupplies can be used, such as particulate or spherical ball extrusionmaterials. The heater softens or melts the extrusion material filamentto form a thermoplastic material that flows into the manifold. When avalve positioned between a nozzle and the manifold is opened, a portionof the thermoplastic material flows from the manifold through the nozzleand is emitted as a stream of thermoplastic material. As used herein,the term “melt” as applied to extrusion material refers to any elevationof temperature for the extrusion material that softens or changes thephase of the extrusion material to enable extrusion of the thermoplasticmaterial through one or more nozzles in an extruder during operation ofa three-dimensional object printer. The melted extrusion material isalso denoted as “thermoplastic material” in this document. As those ofskill in the art recognize, certain amorphous extrusion materials do nottransition to a pure liquid state during operation of the printer.

As used herein, the terms “extruder” refers to a component of a printerthat melts extrusion material in a single fluid chamber and provides themelted extrusion material to a manifold connected to one or morenozzles. Some extruders include a valve assembly that can beelectronically operated to enable thermoplastic material to flow throughnozzles selectively. The valve assembly enables the one or more nozzlesto be connected to the manifold independently to extrude thethermoplastic material. As used herein, the term “nozzle” refers to anorifice in an extruder that is fluidly connected to the manifold in anextruder and through which thermoplastic material is emitted towards amaterial receiving surface. During operation, the nozzle can extrude asubstantially continuous linear swath of the thermoplastic materialalong the process path of the extruder. A controller operates the valvesin the valve assembly to control which nozzles connected to the valveassembly extrude thermoplastic material. The diameter of the nozzleaffects the width of the line of extruded thermoplastic material.Different extruder embodiments include nozzles having a range of orificesizes with wider orifices producing lines having widths that are greaterthan the widths of lines produced by narrower orifices.

As used herein, the term “manifold” refers to a cavity formed within ahousing of an extruder that holds a supply of thermoplastic material fordelivery to one or more nozzles in the extruder during athree-dimensional object printing operation. As used herein, the term“swath” refers to any pattern of the extrusion material that theextruder forms on a material receiving surface during athree-dimensional object printing operation. Common swaths includestraight-line linear arrangements of extrusion material and curvedswaths. In some configurations, the extruder extrudes the thermoplasticmaterial in a continuous manner to form the swath with a contiguous massof the extrusion material in both process and cross-process directions,while in other configurations the extruder operates in an intermittentmanner to form smaller groups of thermoplastic material that arearranged along a linear or curved path. The three-dimensional objectprinter forms various structures using combinations of different swathsof the extrusion material. Additionally, a controller in thethree-dimensional object printer uses object image data and extruderpath data that correspond to different swaths of extrusion materialprior to operating the extruder to form each swath of extrusionmaterial. As described below, the controller optionally adjusts theoperation of the valve assembly and the speed at which the extruder ismoved to form multiple swaths of thermoplastic material through one ormore nozzles during a three-dimensional printing operation.

As used herein, the term “process direction” refers to a direction ofrelative movement between an extruder and a material receiving surfacethat receives thermoplastic material extruded from one or more nozzlesin the extruder. The material receiving surface is either a supportmember that holds a three-dimensional printed object or a surface of thepartially formed three-dimensional object during an additivemanufacturing process. In the illustrative embodiments described herein,one or more actuators move the extruder about the support member, butalternative system embodiments move the support member to produce therelative motion in the process direction while the extruder remainsstationary. Some systems use a combination of both systems for differentaxes of motion.

As used herein, the term “cross process direction” refers to an axisthat is perpendicular to the process direction and parallel to theextruder faceplate and the material receiving surface. The processdirection and cross-process direction refer to the relative path ofmovement of the extruder and the surface that receives the thermoplasticmaterial. In some configurations, the extruder includes an array ofnozzles that can extend in the process direction, the cross-processdirection, or both. Adjacent nozzles within the extruder are separatedby a predetermined distance in the cross-process direction. In someconfigurations, the system rotates the extruder to adjust thecross-process direction distance that separates different nozzles in theextruder to adjust the corresponding cross-process direction distancethat separates the lines of thermoplastic material that are extrudedfrom the nozzles in the extruder as the lines form a swath.

During operation of the additive manufacturing system, an extruder movesin the process direction along both straight and curved paths relativeto a surface that receives thermoplastic material during thethree-dimensional object printing process. Additionally, an actuator inthe system optionally rotates the extruder about the Z axis to adjustthe effective cross-process distance that separates nozzles in theextruder to enable the extruder to form two or more lines ofthermoplastic material with predetermined distances between each line ofthe thermoplastic material. The extruder moves both along the outerperimeter to form outer walls of a two-dimensional region in a layer ofthe printed object and within the perimeter to fill all or a portion ofthe two-dimensional region with the thermoplastic material.

FIG. 6 depicts a prior art three-dimensional object additivemanufacturing system or printer 100 that is configured to operate anextruder 108 to form a three-dimensional printed object 140. The printer100 includes a support member 102, a multi-nozzle extruder 108, extrudersupport arm 112, controller 128, memory 132, X/Y actuators 150, anoptional Zθ actuator 154, and a Z actuator 158. In the printer 100, theX/Y actuators 150 move the extruder 108 to different locations in atwo-dimensional plane (the “X-Y plane”) along the X and Y axes toextrude swaths of thermoplastic material that form one layer in athree-dimensional printed object, such as the object 140 that isdepicted in FIG. 6. For example, in FIG. 6 the X/Y actuators 150translate the support arm 112 and extruder 108 along guide rails 113 tomove the arm and extruder along the Y axis while the X/Y actuators 150translate the extruder 108 along the length of the support arm 112 tomove the extruder along the X axis. The extruded patterns include bothoutlines of one or more regions in the layer and swaths of thethermoplastic material that fill the regions within the outline ofthermoplastic material patterns. The Z actuator 158 controls thedistance between the extruder 108 and the support member 102 along the Zaxis to ensure that the nozzles in the extruder 108 remain at a suitableheight to extrude thermoplastic material onto the object 140 as theobject is formed during the printing process. The Zθ actuator 154controls an angle of rotation of the extruder 108 about the Z axis forsome embodiments of the extruder 108 that rotate about the Z axis. Thismovement controls the separation between nozzles in the extruder 108,although some extruders do not require rotation during the manufacturingprocess. In the system 100, the X/Y actuators 150, Zθ actuator 154, andthe Z actuator 158 are embodied as electromechanical actuators, such aselectric motors, stepper motors, or any other suitable electromechanicaldevice. In the printer of FIG. 6, the three-dimensional object printer100 is depicted during formation of a three-dimensional printed object140 that is formed from a plurality of layers of thermoplastic material.

The support member 102 is a planar member, such as a glass plate,polymer plate, or foam surface, which supports the three-dimensionalprinted object 140 during the manufacturing process. In the embodimentof FIG. 2, the Z actuator 158 also moves the support member 102 in thedirection Z away from the extruder 108 after application of each layerof thermoplastic material to ensure that the extruder 108 maintains apredetermined distance from the upper surface of the object 140. Theextruder 108 includes a plurality of nozzles and each nozzle extrudesthermoplastic material onto the surface of the support member 102 or asurface of a partially formed object, such the object 140. In theexample of FIG. 6, extrusion material is provided as a filament fromextrusion material supply 110, which is a spool of ABS plastic oranother suitable extrusion material filament that unwinds from the spoolto supply extrusion material to the extruder 108.

The support arm 112 includes a support member and one or more actuatorsthat move the extruder 108 during printing operations. In the system100, one or more actuators 150 move the support arm 112 and extruder 108along the X and Y axes during the printing operation. For example, oneof the actuators 150 moves the support arm 112 and the extruder 108along the Y axis while another actuator moves the extruder 108 along thelength of the support arm 112 to move along the X axis. In the system100, the X/Y actuators 150 optionally move the extruder 108 along boththe X and Y axes simultaneously along either straight or curved paths.The controller 128 controls the movements of the extruder 108 in bothlinear and curved paths that enable the nozzles in the extruder 108 toextrude thermoplastic material onto the support member 102 or ontopreviously formed layers of the object 140. The controller 128optionally moves the extruder 108 in a rasterized motion along the Xaxis or Y axis, but the X/Y actuators 150 can also move the extruder 108along arbitrary linear or curved paths in the X-Y plane.

The controller 128 is a digital logic device such as a microprocessor,microcontroller, field programmable gate array (FPGA), applicationspecific integrated circuit (ASIC) or any other digital logic that isconfigured to operate the printer 100. In the printer 100, thecontroller 128 is operatively connected to one or more actuators thatcontrol the movement of the support member 102 and the support arm 112.The controller 128 is also operatively connected to a memory 132. In theembodiment of the printer 100, the memory 132 includes volatile datastorage devices, such as random access memory (RAM) devices, andnon-volatile data storage devices such as solid-state data storagedevices, magnetic disks, optical disks, or any other suitable datastorage devices. The memory 132 stores programmed instruction data 134and three-dimensional (3D) object image data 136. The controller 128executes the stored program instructions 134 to operate the componentsin the printer 100 to form the three-dimensional printed object 140 andprint two-dimensional images on one or more surfaces of the object 140.The 3D object image data 136 includes, for example, a plurality oftwo-dimensional image data patterns that correspond to each layer ofthermoplastic material that the printer 100 forms during thethree-dimensional object printing process. The extruder path controldata 138 include a set of geometric data or actuator control commandsthat the controller 128 processes to control the path of movement of theextruder 108 using the X/Y actuators 150 and to control the orientationof the extruder 108 using the Zθ actuator 154. The controller 128operates the actuators to move the extruder 108 above the support member102 as noted above while the extruder extrudes thermoplastic material toform an object.

FIG. 1 depicts an additive manufacturing system 100′ having an extruder108 that extrudes a plurality of thermoplastic materials throughapertures in a faceplate as shown in FIG. 3 and FIG. 4, which isdescribed in more detail below. Although the printer 100′ is depicted asa printer that uses planar motion to form an object, other printerarchitectures can be used with the extruder and the controllerconfigured to regulate speed of the extruder with reference to theangular orientation of the extruder as described in this document. Thesearchitectures include delta-bots, selective compliance assembly robotarms (SCARAs), multi-axis printers, non-Cartesian printers, and thelike. The motions in these alternative embodiments still have processand cross-process directions as defined above and the nozzle spacing inthe extruders of these embodiments still define the nozzle spacing withrespect to the cross-process direction. Only one manifold 216 is shownin FIG. 1 to simplify the figure, but the extruder 108 can have aplurality of manifolds 216. In one embodiment, each manifold 216 in theextruder 108 is operatively connected to a different heater 208 that isfed by a different extrusion material supply 110 in a one-to-onecorrespondence. Alternatively, each manifold 216 can be coupled to asingle heater 208′ that houses a plurality of channels 232′ that are fedby a plurality of extrusion material supplies 110 as shown in theembodiment 100″ of FIG. 2. Each channel 232′ in FIG. 2 suppliesthermoplastic material to a manifold 216 in the extruder 108 to enableeach manifold to receive a material that is different than a materialthat the other manifolds are receiving. In the extruder 108, each nozzle218 is fluidly connected to only one of the manifolds within theextruder 108 so each nozzle can extrude a thermoplastic material that isdifferent than the materials extruded from nozzles connected to othermanifolds. Extrusion from each nozzle is selectively and independentlyactivated and deactivated by controller 128 operating the valves in thevalve assembly 204. Each nozzle 218 is also aligned with an aperture ina faceplate 260 to configure the nozzles for more flexible formation ofswaths of the materials in an object.

In the embodiments of FIG. 1 and FIG. 2, a valve assembly 204 positionsa valve between the manifolds in the extruder 108 and each of thenozzles connected to the manifolds in the extruder 108. The valveassembly 204 is operatively connected to the controller 128 so thecontroller can open and close the valves for extruding thermoplasticmaterial from the plurality of nozzles in the extruder 108.Specifically, the controller 128 activates and deactivates differentactuators in the assembly 204 connected to the valves in the extruder108 to extrude thermoplastic material from the nozzles and form swathsof different thermoplastic materials in each layer of athree-dimensional printed object, such as object 140 in FIG. 6.

The system 100′ of FIG. 1 also includes an extrusion material dispensingsystem 212 for each heater 208 that is connected to a manifold in theextruder 108. The extrusion material from each separate supply 110 isfed to the corresponding heater 208 at a rate that maintains thepressure of the thermoplastic material in the manifold connected to theheater within a predetermined range during operation of the system 100′.The dispensing system 212 is one embodiment that is suitable forregulating pressure of the thermoplastic material in each manifold ofthe extruder 108. In embodiment 100″ of FIG. 2, a plurality of extrusionmaterial dispensing systems 212 are operatively connected between aplurality of extrusion material supplies 110 and a channel 232′ in theheater 208′ in a one-to-one correspondence. Additionally, in bothembodiments, the controller 128 is operatively connected to an actuatoreach dispensing system 212 to control the rate at which the dispensingsystem 212 delivers extrusion material from a supply 110 to the heaterfed by the supply. The dispensing systems 212 of FIG. 2 can beconfigured as the dispensing system 212 of FIG. 1. The heaters 208 and208′ soften or melt the extrusion material 220 fed to the heater 208 viadrive roller 224 (FIG. 1). Actuator 240 drives the roller 224 and isoperatively connected to the controller 128 so the controller canregulate the speed at which the actuator drives the roller 224. Anotherroller opposite roller 224 is free-wheeling so it follows the rate ofrotation at which roller 224 is driven. While FIG. 1 depicts a feedsystem that uses an electromechanical actuator and the driver roller 224as a mechanical mover to move the filament 220 into the heater 208 or208′, alternative embodiments of the dispensing system 212 use one ormore actuators to operate a mechanical mover in the form of a rotatingauger or screw. The auger or screw moves solid phase extrusion materialfrom a supply 110 in the form of extrusion material powder or pelletsinto a heater 208 or 208′.

In the embodiments of FIG. 1 and FIG. 2, each heater has a body formedfrom stainless steel that includes one or more heating elements 228,such as electrically resistive heating elements, which are operativelyconnected to the controller 128. Controller 128 is configured to connectthe heating elements 228 to electrical current selectively to soften ormelt the filament of extrusion material 220 in the channel or channelswithin the heater 208 or 208′. While FIG. 1 and FIG. 2 show heater 208and heater 208′ receiving extrusion material in a solid phase as solidfilament 220, in alternative embodiments, the heaters receive theextrusion material in solid phase as powdered or pelletized extrusionmaterial. Cooling fins 236 attenuate heat in the channels upstream fromthe heater. A portion of the extrusion material that remains solid in achannel at or near the cooling fins 236 forms a seal in the channel thatprevents thermoplastic material from exiting the heater from any openingthan the connection to the manifold 216, which maintains a temperaturethat keeps the extrusion material in a thermoplastic state as it entersthe manifold. The extruder 108 can also include additional heatingelements to maintain an elevated temperature for the thermoplasticmaterial within each manifold within the extruder. In some embodiments,a thermal insulator covers portions of the exterior of the extruder 108to maintain a temperature within the manifolds within the extruder.Again, the regions around the nozzles in FIG. 2 are maintained at atemperature that keeps the material in a thermoplastic state so it doesnot begin solidifying as it travels to the apertures in the faceplate.

To maintain a fluid pressure of the thermoplastic material within themanifolds 216 within a predetermined range, avoid damage to theextrusion material, and control the extrusion rate through the nozzles,a slip clutch 244 is operatively connected to the drive shaft of eachactuator 240 that feeds filament from a supply 110 to a heater. As usedin this document, the term “slip clutch” refers to a device appliesfrictional force to an object to move the object up to a predeterminedset point. When the range about the predetermined set point for thefrictional force is exceeded, the device slips so it no longer appliesthe frictional force to the object. The slip clutch enables the forceexerted on the filament 220 by the roller 224 to remain within theconstraints on the strength of the filament no matter how frequently,how fast, or how long the actuator 240 is driven. This constant forcecan be maintained by either driving the actuator 240 at a speed that ishigher than the fastest expected rotational speed of the filament driveroller 224 or by putting an encoder wheel 248 on the roller 224 andsensing the rate of rotation with a sensor 252. The signal generated bythe sensor 252 indicates the angular rotation of the roller 224 and thecontroller 128 receives this signal to identify the speed of the roller224. The controller 128 is further configured to adjust the signalprovided to the actuator 240 to control the speed of the actuator. Whenthe controller is configured to control the speed of the actuator 240,the controller 128 operates the actuator 240 so its average speed isslightly faster than the rotation of the roller 224. This operationensures that the torque on the drive roller 224 is always a function ofthe slip clutch torque.

The controller 128 has a set point stored in memory connected to thecontroller that identifies the slightly higher speed of the actuatoroutput shaft over the rotational speed of the roller 224. As used inthis document, the term “set point” means a parameter value that acontroller uses to operate components to keep the parametercorresponding to the set point within a predetermined range about theset point. For example, the controller 128 changes a signal thatoperates the actuator 240 to rotate the output shaft at a speedidentified by the output signal in a predetermined range about the setpoint. In addition to the commanded speed for the actuator, the numberof valves opened or closed in the valve assembly 204 and the torque setpoint for the clutch also affect the filament drive system 212operation. The resulting rotational speed of the roller 224 isidentified by the signal generated by the sensor 252. Aproportional-integral-derivative (PID) controller within controller 128identifies an error from this signal with reference to the differentialset point stored in memory and adjusts the signal output by thecontroller to operate the actuator 240. Alternatively, the controller128 can alter the torque level for the slip clutch or the controller 128can both alter the torque level and adjust the signal with which thecontroller operates the actuator.

The slip clutch 244 can be a fixed or adjustable torque friction discclutch, a magnetic particle clutch, a magnetic hysteresis clutch, aferro-fluid clutch, an air pressure clutch, or permanent magneticclutch. The clutch types that operate magnetically can have their torqueset points adjusted by applying a voltage to the clutches. This featureenables the torque set point on the clutch to be changed with referenceto print conditions. The term “print conditions” refers to parameters ofthe currently ongoing manufacturing operation that affect the amount ofthermoplastic material required in the manifold for adequate formationof the object. These print conditions include the type of extrusionmaterial being fed to the extruder, the temperature of the thermoplasticmaterial being emitted from the extruder, the speed at which theextruder is being moved in the X-Y plane, the position of the featurebeing formed on the object, the angle at which the extruder is beingmoved relative to the platform, and the like.

In the embodiments shown in FIG. 1 and FIG. 2, the controller 128 isconfigured to transmit one or more signals to the X/Y actuators 150 toregulate the speed at which the extruder 108 is moved above platform102. The controller 128 is configured to regulate the speed of theextruder 108 with reference to the angle of the path at which theextruder 108 is to be moved and the orientation of the extruderfaceplate as it moves along that path. When the extruder 108 is movedduring extrusion in either direction along the 0°-180° axis or the90°-270° axis and the extruder faceplate is oriented as shown in FIG. 7,the controller 128 moves the extruder at a nominal speed with referenceto the number of nozzles opened for the extrusion of thermoplasticmaterial. Although an extruder face can theoretically be oriented so allof the opened nozzles contribute to a contiguous swath along any motionpath, practical considerations can prevent such orientations. Whenobject image data and extruder path data require an orientation for theextruder faceplate and its motion path relative to the platform thatinterferes with the ability of the extruder to form a contiguous swath,the controller can reduce the speed at which the extruder is moved alongthat motion path relative to the platform to address this interference.

As noted above, the gaps produced between the lines forming a swathgenerated by the nozzles in the faceplate depicted in FIG. 7 aregreatest when the extruder faceplate is oriented as shown and the angleof extruder motion is along one of the 18°, 108°, 198°, and 288° paths.FIG. 3 depicts the operation of an extruder head in which the nozzles inthe faceplate are the mirror image of the nozzle arrangement in FIG. 7.When this type of extruder head is moved along one of the 72°, 162°,252°, and 342° paths, the rows and columns of the nozzle array areorthogonal to one another and the nozzles produce a swath having threeseparate lines when all nine nozzles are opened. FIG. 3 illustrates theeffect of speed regulation in either direction along the 162°-342° pathfor such an extruder. The base 304 has been printed at 0°-180° using anextruder having a nine-nozzle faceplate that is oriented and moved asdepicted in FIG. 7. The diagonal swaths are printed on the base 304along the 162°-342° path at which groups of three nozzles aligncoincidentally. The diagonal swaths are printed in the order 308, 312,316, 320, 324, and 328 with swaths 308, 316, and 324 being printed asthe extruder moves along the 162° path and with swaths 312, 320, and 328being printed as the extruder moves along the 342° path. That is, theextruder 108 is oriented as shown by the two middle faceplates in FIG. 7and is moved along the 162° path until it reaches a stop position whereit is translated at 90° without extruding any material and then isreturned along the 342° path until it reaches another stop positionwhere it is translated at 90° without extruding any material to reach aposition for forming the next pair of swaths. Swaths 308 and 312 wereformed with nine open nozzles, swaths 316 and 320 were formed with sixopen nozzles, and swaths 324 and 328 were formed with three opennozzles. Each diagonal swath is printed so the extruder is moving at ⅓of the nominal speed at the left portion of the swarth, at ⅔ of thenominal speed at the center portion of the swath, and at the nominalspeed at the right portion of the swath. The nominal speed in thisexample is 4000 mm/min.

As shown in FIG. 3, moving the extruder oriented as described abovealong the 162°-342° path at the nominal speed does not enable the linesof the extruded thermoplastic material emitted from the open nozzles tospread enough to fill the gaps and make a contiguous swath in thecross-process direction. The size of the gap depends on the number ofopen nozzles and the speed of the extruder. As the speed is reduced ineach swath, the amount of material extruded and the extent ofthermoplastic material spread increases as can be seen in the center andleft portions of the swaths. As shown in the figure, the swaths formedby moving the extruder along the 162° path differ in the amount ofmaterial spread than those formed by moving the extruder along the 342°path. This difference may be due in part to the order of printing and inpart to a misalignment of the extruder. This effect indicates that someamount of extruder misalignment can be compensated by changing the speedof the extruder as it moves. To compensate for misalignment, amisalignment parameter is determined during a printer calibration andthat parameter is stored in the memory operatively connected to thecontroller 128. During object printing, the controller 128 adjusts thespeed for the extruder with reference to the misalignment parameter.FIG. 3 also reveals that the width of a swath is not necessarilyindependent of angle of extruder movement. For the angle shown in thefigure, the width of the swath is ideally three times the spacingbetween the column of nozzles at the angle of rotation plus three timesthe width of a single nozzle. The spacing width at the angle of rotationis 0.865 mm. Thus, for the nine-nozzle configuration at the rotatedangle used to form the swaths in FIG. 3, the width of a swath is:1.265×3, which is approximately 3.8 mm.

In FIG. 4, another set of swaths 408, 412, 416, 420, 424, and 428 havebeen printed along the 162-342° path with the same number of nozzleswith an extruder having a nozzle array arranged as explained above withregard to FIG. 3. Swaths 408 and 412 are printed at ⅔ of the nominalspeed, swaths 416 and 420 are printed at ½ nominal speed, and swaths 424and 428 are printed at ⅓ nominal speed. The number of opened nozzles onthe various paths remains as described above with regard to FIG. 3.Thus, all portions of each swath have been formed at some speed that isless than the nominal speed. The resulting spreads, which are greaterthan those produced at the nominal speed in FIG. 3, indicate that evenat the angles that produce the greatest gaps between lines within aswath, the regulation of extruder speed can compensate for thenon-optimal layout of the nozzles and that regardless of the gap width,the extruder speed can be reduced to a level that maintains contiguousswaths in the cross-process direction without having to print the regionwith multiple passes. FIG. 4 also shows that the gaps between lines canbe reduced by increasing the number of open nozzles aligned with theprinting direction. Empirical experimentation is used to establish theoptimal speeds for all of the extruder motion angles that align nozzlesfor a particular faceplate configuration. Other extruder motion anglesrequire less reduction in speed than these angles that depend on theprojection of the spacing between nozzles as the extruder moves in theprocess direction.

The results depicted in FIG. 3 and FIG. 4 show that, regardless of thenominal extruder movement speed, slower movement speed enables greaterflow through the nozzles of a faceplate. The flow through the nozzles atthe nominal extruder speed is enabled by maintaining the pressure in thenozzles established for the preferred extruder faceplate orientation andmovement angles of 0°, 90°, 180°, and 270°. This pressure needs to behigher for faster extruder movement speeds at these angles for movementand lower for slower extruder movement speeds at these angles formovement to get the same contiguous swath width in the cross-processdirection. To achieve this effect, enough filament is fed into theheater to maintain the appropriate predetermined pressure at theseangles. When the extruder is oriented and moved along paths at angleswhere multiple nozzles are aligned, such as 72° for the extruder used toform the swaths in FIG. 3 and FIG. 4, the requisite higher pressure ismaintained by feeding the required amount of filament and moving at theempirically determined speed for extruding that amount of filament.Thus, a balance is maintained between thermoplastic material pressure inthe extruder and the amount of thermoplastic material extruded from theextruder. If speed of the extruder is adjusted to match the amount offilament fed to the heater of the extruder, then the amount of materialextruded is also adjusted to preserve the pressure/extruded amountequilibrium.

FIG. 5 depicts a block diagram of a process 500 for operation of aprinter that adjusts the speed of extruder movement with reference to anangle of extruder movement. In the discussion below, a reference to theprocess 500 performing a function or action refers to the operation of acontroller, such as controller 128, to execute stored programinstructions to perform the function or action in association with othercomponents in the printer. The process 500 is described in conjunctionwith the printer 100′ of FIG. 1 and printer 100″ of FIG. 2 forillustrative purposes.

The process 500 begins with the controller retrieving object image datafor a swath in a layer of an object being made (block 504). Thecontroller identifies a relative path of movement between the extruderand the platform as well as the number of nozzles that are to be openduring the movement of the extruder (block 508). The identified relativepath of movement includes identifying the orientation of the extruderfaceplate as it moves along the path. The process then identifies aspeed for the relative movement between the extruder and the platformwith reference to an angle for the relative path (block 512). Thecontroller then operates the filament movers for the extrusion materialfilament supplies that supply filament to the heater channels connectedto the manifolds for the open nozzles, operates the X/Y actuators tomove the extruder along the relative path for the extruder withreference to the identified speed, and operates the valve assembly toopen the identified nozzles (block 520). While the swath is being formed(block 524), the controller continues to operate these componentsaccordingly (block 520). When the swath is complete (block 524), theprocess determines whether the layer is complete (block 528), and if itis not complete, it retrieves the object image data for the next swathin the layer (block 504). Otherwise, the process determines if the lastlayer of the object has been formed (block 532), and if it has beenformed, the process stops. Otherwise, the process adjusts the positionof the extruder relative to the platform along the Z axis and retrievesthe object image data for the next layer (block 536) so the printing ofthe next layer can occur (blocks 504 to 528).

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems, applications or methods.Various presently unforeseen or unanticipated alternatives,modifications, variations or improvements may be subsequently made bythose skilled in the art that are also intended to be encompassed by thefollowing claims.

What is claimed:
 1. An apparatus comprising: a platform configured tosupport an object during manufacturing; an extruder having a pluralityof nozzles; at least one actuator operatively connected to at least oneof the extruder and the platform, the at least one actuator beingconfigured to move the at least one of the extruder and the platformrelative to the other of the extruder and the platform; and a controlleroperatively connected to the extruder and the at least one actuator, thecontroller being configured to: operate the extruder using object imagedata and extruder path data to extrude thermoplastic material through atleast two of the nozzles of the extruder to form a swath ofthermoplastic material along a path of relative movement between theextruder and the platform; operate the at least one actuator to move theat least one of the extruder and the platform along the path of relativemovement at a predetermined speed; select an angle for the path ofrelative movement between the extruder and the platform to be a firstangle when the swath of thermoplastic material is placed within aninterior portion of the object and to select the angle of the path ofrelative movement to be a second angle when the swath of thermoplasticmaterial is placed on the exterior of the object, the first angle beingdifferent than the second angle; select the predetermined speed for thepath of relative movement between the extruder and the platform to beless than a nominal speed of the extruder using an orientation of afaceplate of the extruder and the selected angle for the path ofrelative movement between the extruder and the platform to make theswath of the thermoplastic material contiguous in a cross-processdirection when movement of the extruder with the orientation of thefaceplate of the extruder along the selected angle of the path ofrelative movement at the nominal speed produces gaps between thethermoplastic material extruded from the at least two different nozzles;select a number of nozzles in the extruder for extrusion of thethermoplastic material, the selected number of nozzles being at leasttwo nozzles and up to all of the nozzles in the plurality of nozzles;and adjust the selected predetermined speed using the selected number ofnozzles.
 2. The apparatus of claim 1 wherein the predetermined speed isone-half of the nominal speed of the extruder when the orientation ofthe extruder faceplate and the path of relative movement is at an anglethat arranges the plurality of nozzles in the faceplate into an arrayhaving orthogonal columns and rows.
 3. The apparatus of claim 1, thecontroller being further configured to: adjust the predetermined speedfor movement of the extruder along the path of relative movement using amisalignment parameter for the extruder.
 4. The apparatus of claim 1,the controller being further configured to: select the first angle to bea 0°-180° axis or a 90°-270° axis for the path of relative movementbetween the extruder and the platform.
 5. The apparatus of claim 1further comprising: a plurality of extrusion material supplies; a heaterhaving a plurality of channels, each channel of the heater beingoperatively connected to only one extrusion material supply in theplurality of extrusion material supplies in a one-to-one correspondencebetween the plurality of channels and the plurality of extrusionmaterial supplies and each channel in the heater being operativelyconnected to only one manifold in the extruder in a one-to-onecorrespondence between the plurality of channels and a plurality ofmanifolds in the extruder so thermoplastic material produced by eachchannel enters the manifold to which the channel is operativelyconnected; a plurality of mechanical movers, each mechanical mover beingconfigured to move extrusion material from one of the extrusion materialsupplies to the corresponding one of the channels in the heater, eachmechanical mover also being configured for independent control of a rateat which the extrusion material is supplied to the corresponding onechannel in the heater; and the controller being further configured to:operate each mechanical mover corresponding to one of the selectednozzles to move extrusion material into the corresponding channel in theheater at a predetermined rate that maintains a predetermined pressurein the corresponding manifold while the extruder is moved at theselected predetermined speed.
 6. The apparatus of claim 5, thecontroller being further configured to: select the predetermined speedto be greater than the nominal speed; and increase the predeterminedrate when the selected predetermined speed is greater than the nominalspeed.